What does 1 Corinthians 6:20 mean?

Paul now concludes his teaching on why it matters that Christians run away from sexual immorality. His final point, begun in the previous verse, is that Christian people do not belong to themselves. We have been purchased by God. We are free in the sense that we have been freed from the law of sin and death (Galatians 3:13), but we are not free in the sense that we are now self-owned and self-determined (1 Corinthians 6:12–13).

If we are truly in Christ, we are truly not our own. Our lives, including our bodies, belong to God. This gives Him the ultimate authority to tell us what to do and what not to do with our bodies.

It's important to notice something about this last argument against sexual immorality. It applies only to believers. Only those in Christ have been redeemed by His blood and brought from darkness to light (1 Corinthians 1:12–13). These words are not for those who remain in darkness. Paul is not commanding those outside the church, unbelievers, to live according to God's standards for sexual morality (1 Corinthians 5:12). Their sin is still sin, but one cannot expect them to recognize it as such (1 Corinthians 2:14).

Rather, it is those who belong to God—and not to themselves—who are commanded to glorify God with their bodies. In fact, only those in Christ have an opportunity to use their bodies to bring glory to God. In fact, that is now the purpose our bodies are designed to serve. Selfishly participating in sexual sin keeps us Christians from fulfilling our purpose.